a better question to ask is why it is that democratic candidates didn't see this coming. i want you to go back and watch the 2020 debates and tell me with a straight face that he looked capable and competent. he didn't. so, why didn't anybody primary him? the answer is that nobody thought they could win, and they were probably right. still. even after his resignation, biden would still win primaries against virtually anybody running, with the possible exception of bernie sanders.
this is a "it's not me, it's you" type situation, from the perspective of voters. biden won in the first place because the field was horrific. harris ended up as vp because there was nobody else willing to do it. for all the rhetoric about choices from an identity politics marketing perspective, the reality is that the party doesn't have many popular candidates that can win close elections in contested districts, because you could never raise enough money to run, if you actually had popular support. it's a catch-22.
so, the country ends up stuck with the bidens in the spectrum, and keeps voting for them, even after they're senile, and even after they've resigned.
i'm cringing at harris, but they are correct on some level. they need to build grassroots support. but, they're going to do that by focusing on populist economic messaging and presenting a serious candidacy, not on stupid pop culture memes that make her look desperate and half-retarded. presidents should spend the summer getting shitfaced and falling down the stairs. right. and, the actual truth is that this woman is so right-wing, the uk tories would tell her to fuck off and go call nigel farage. she's too conservative for the tories; they'd call her an extremist. you'd think these people could figure that out, but they can't and they're probably never going to.
so, the american people need to figure it out for them and organize on their own. i would advise choosing the green party as the vehicle to do it with.